In the early long term evolution (LTE) system, both uplink and downlink of a user equipment (UE) can only be served by one carrier. With the progress of standards, the carrier aggregation (CA) technology is introduced, at this point one UE may be served by multiple uplink carriers simultaneously, and may also be served by multiple downlink carriers simultaneously, so as to improve the peak data rate of the UE. All early carrier aggregation systems are the aggregation of carriers under the same base station, or the carrier aggregation of a macro cell and a micro cell having ideal backhaul. Where, two nodes having ideal backhaul can be seen as the same base station. Where, the ideal backhaul means that the transmission delay of the backhaul is very small and can be ignored, for example, the backhaul of a macro base station and a micro base station which is constituted via fiber-optic links, where the delay among multiple nodes connected via these fiber-optic links is very small. In this case, when scheduling one carrier of the aggregation carriers, the base station can know in real time the scheduling condition on another carrier, therefore, the joint scheduling can be adopted among these carriers. In an existing CA system, acknowledge (ACK,) or non-acknowledge (NACK) corresponding to the downlink data scheduling is born on the physical uplink control channel (PUCCH), the PUCCH is only transmitted on one uplink carrier, this uplink carrier is called the uplink primary carrier, and the sequence related information of this PUCCH is determined by the cell identity corresponding to this uplink carrier.
In the existing CA system, there are two kinds of PUCCH feedback modes, one is a feedback mode of PUCCH format 1b in combination with channel selection, and the other is a feedback mode of PUCCH format 3.
For the feedback mode of PUCCH format 1b in combination with channel selection:
The data born on the PUCCH format 1b channel is constituted by the cyclic shift of a Zad-off Chu (ZC) sequence in the frequency domain, and is constituted by the ACK or NACK multiplied by one spreading code in the time domain. Different PUCCH format 1b channels of one resource block (RB) are distinguished through the abovementioned cyclic shift of the ZC sequence and the time-domain spreading code, that is, one PUCCH format 1b channel includes one cyclic shift of ZC sequence and one time-domain spreading code, where the ZC sequence is determined by the cell identity corresponding to the uplink carrier which transmits this PUCCH. The channel selection is that the same PUCCH information (such as modulation symbol) transmitted on different PUCCH channels means different information, such as the same modulation symbol transmitted on the PUCCH format 1b channel 1 means ACK, while the same modulation symbol transmitted on the PUCCH format 1b channel 2 means NACK.
For downlink scheduling of the primary carrier, the way of allocating the PUCCH format 1b channel resource specifically includes: the PUCCH format 1b channel resource is determined implicitly through a corresponding PDCCH parameter, for example, the PUCCH format 1b resource is determined through the CCE index of the PDCCH, or the PUCCH format 1b resource is determined through the eCCE index of the ePDCCH and/or the antenna port number, etc.; to facilitate the description, hereinafter, the PDCCH and ePDCCH are both expressed as PDCCH; for downlink scheduling of the secondary carrier, the solution of high-level reserve in combination with PDCCH dynamic selection is adopted as the way of allocating the PUCCH format 1b resource, which specifically includes: the PUCCH format 1b channel resource is configured as four groups of channel resources through a radio resource control (RRC) signaling, and the base station dynamically indicates to the UE, through scheduling two bits of the PDCCH of the secondary carrier, one group of these four groups of channel resources for current use.
For the feedback mode of PUCCH format 3:
The PUCCH format 3 has no cyclic shift of the ZC sequence in the frequency domain, but has the spreading code in the time domain, where different PUCCH format 3 channel resources of one resource block are distinguished through the abovementioned spreading code. Different cyclic shift code of the modulation symbol which is spread by using the time-domain spreading code can be adopted for the PUCCH format 3 channels on different orthogonal frequency division multiplexing (OFDM) symbols of one sub-frame. Which cyclic shift code being adopted is determined upon the cell identity corresponding to the uplink carrier of this PUCCH.
The solution of high-level reserve in combination with PDCCH dynamic selection is adopted as the way of allocating the PUCCH format 3 channel resource, which specifically includes: the PUCCH format 3 channel resource may be configured as four resources through the RRC signaling, and the base station dynamically indicates to the UE, through scheduling two bits of the PDCCH of the secondary carrier, one of these four resources for current use.
In the subsequently evolved LTE system, the carrier aggregation among base stations having non-ideal backhaul will be introduced, that is, it is impossible to transfer data among base stations in real time, which results in that the scheduling among multiple carriers belonging to different base stations is performed independently, that is, when one base station schedules one carrier of the aggregation carriers, the base station does not know the condition on another carrier which is scheduled by another base station.
For example: the macro cell deployed at frequency f1 mainly provides system information and performs radio link monitoring and mobility management, so as to ensure continuity of services; multiple micro cells deployed at frequency f2 mainly provides the transmission of high data rate services, and the multiple micro cells are in the coverage range of the macro cell. The backhaul among the abovementioned macro cell and micro cells, or among the micro cells are all non-ideal backhaul, that is, the information cannot be interacted in real time.
In the abovementioned CA system among base stations having non-ideal backhaul, since the data scheduling of multiple downlink carriers is performed independently by each base station, for example, the macro base station at frequency f1 and the micro base station at frequency f2 schedule independently, one direct solution is transmitting multiple PUCCHs on multiple carriers respectively, so that the ACK or NACK can be fed back to respective base station respectively. However, the uplinks of some low-end UEs do not have the capacity of transmitting multiple carriers; even if the uplinks of some high-end UEs have the capacity of transmitting multiple carriers, when the UE power is limited, transmitting multiple PUCCHs simultaneously will affect the PUCCH performance.